Knife blade type fuse having silverplated blade contacts



May 19, 1964 P. C. HITCHCOCK 3,134,001

KNIFE BLADE TYPE FUSE HAVING SILVER-PLATED BLADE CONTACTS Fig.3

Fig 4 V//// NN BY MN NN,

May 19, 1964 P. C. HITCHCOCK KNIFE BLADE TYPE FUSE HAVING SILVER-PLATED BLADE CONTACTS 2 Sheets-Sheet 2 Filed March 21, 1961 Fig.7

7u 7o To Fig.9

INVENTOR. C. WM Bynmwmkw United States Patent Oii ice n 3,134,001 Patented May '719, 19'6`4 3,134,001 KNIFE BLADE TYPE FUSE HAVING SILVER- PLATED BLADE CONTACTS Paul C. Hitchcock, Plum Island, Mass., assiguor to The Chase-Shawmut Company, Newburyport, Mass. Filed Mar. 21, 1961, Ser. No. 97,269 2 Claims. (Cl.`200-132) This invention relates to electric fuses and to a process for manufacturing the same.

From a more limited point of viewthis invention relates to fuses having ribbon type fusible elements and blade type contacts which include a relatively large mass of solid copper. K

In certain instances the mechanical and electrical joint required between the fusible element or fuse link and a blade contact of a fuse can readily be established, but in other instances establishing this joint involves serious diiculties. y

Where the mass of the blade type contacts is relatively small, the aforementioned joint can readily be established by spotwelding. The spotwelding method involves, however, great difficulties in instances where blade type contacts include a relatively large mass of solid copper. It is practically impossible to heat a large mass of copper to the temperature required for establishing a normal spot- Mechanical joints are not as stable as joints involving l i` the fusion of metals. A soft solder joint is rather `difficult to achieve between a ribbon type fuse link and a blade type contact when the latter includes a relatively large mass of copper. The diiculties of making such a joint are practically insurmountable if the condition is imposed that the soft solder must not extend over the area of overlap between the ribbon type fusible element or link and the blade type contact. It is, however, often necessary to impose this condition as, for instance, when the surfaces of the blade type contact have beenmachined to adapt them to cooperate with certain fastener means, in which case the machined surfaces might be impaired by an outiiow of solder from the area of overlap between the fusible element or link and the blade type contact.

Brazing of joints of the aforementioned character is about as difficult as making the same by soft soldering, and brazing compounds have the same tendency as soft solders to ilow out of the area of overlap between the ribbontype fusible element and the blade type Contact and to impair machined surfaces on the latter.

As far as l am aware no wholly satisfactory joint has ever been achieved between ribbon type fusible elements or fuse links and blade type contacts which include a relatively large mass of copper, i.e. such a large mass of copper as to prohibit establishing normal spotwelds between the fusible element and the blade type contacts.

It is, therefore, one object of this invention to provide electric fuses having an improved and wholly satisfactory electrical and mechanical connection, or joint, between `a pair of massive blade contacts of copper anda ribbon type fuse link of copper.

Another object of this invention is to provide electric fuses having massive blade contacts of copper which are silver plated to preclude the oxidation of their surfaces, or the formation of copper oxide thereon, wherein an additional function is assigned to the silver plating, namely the function of establishing a stable current path from the blade contact to the fuse link.

Still another object of the invention is to provide electric fuses having ribbon type fuse links brazed to massive blade contacts of copper, wherein the brazing joint is coextensive with the area of overlap between the fuse links and the blade contacts, and wherein no brazing metal is spilled beyond this area.

These and other objects of the invention and advantages thereof will become more apparent from the accompanying drawings and the following description of a preferred embodiment of the invention. In the drawings FTGS. l-4 illustrate diagrammatically sequential steps involved in a process of making fuses according to this invention;

FIG. 5 is a flow chart of that process; n f

FIG. 6 is a side elevation of a subassembly manufactured by the process of FIGS. 1-5;

FIG. 7 is a top-planview of the structure of FIG. 6;

FIG. 8 is a longitudinal section of a complete fuse embodying this invention taken along 8-8 of FIG. 9; and

FIG. 9 is a section along 9-9 of FIG. r8.

Referring now to the'drawings, and more particularly FIGS. lfS thereof, the first step in the process consists in reducing arelatively ylong copper bar 1 into sections 1 of relatively short length. This can best be achieved by means kof a suitable punch press (not shown). The relatively short sections 1 are then transferred into a galvanic plating bath 2 wherein they may be suspended from rod 3 on hooks 4. Rod 3 forms the positive electrode. Reference numeral 3 has been applied to indicate the negative electrode. The holes in sections 1 used to suspend sections 1 on hooks 4 may be produced by the same punching operation used for chopping, or sectionalizing, copper bar 1. The copper sections 1' are intended to form knife blade contacts in a fuse structure. To this end fuse link means must be attached to one end of sections 1 and a highly conductive current path must beestablished between the fuse link means and sections 1'; If sections 1 were made of relatively thin copper, as by chopping a long coppertube rectangular infcross-Section into sections of short lengths, the fuse link means could readily be connected to such sections by spotwelding. This process cannot readily be applied if the mass of sections 1 is relatively large, as in case of heavy blade contacts intended to carry relatively large currents, or intended to have a relatively large heaty absorbing capacity. According to this invention ribbon type copper links are being silver brazed to silver plated copper contacts, the silver plating of the latter being used to braze the copper links to the contacts. To this end silver plated sections 1 are, in part, sandwiched between the axially outer ends of a pair of aligned and superimposed ribbon fuse links 7 of copper and sections 1 and links 7 are clamped between a `pair of high resistance brushes 6 as, for instance, carbon brushes, each supported by a brush holder 5. Brushes 6 form part of the secondary circuit of a transformer, generally designated by the reference character 9. Transformer 9 comprises the secondary winding 10 and the primary winding 11. The latter is connected to electric system 13 by the intermediary of an electrictimer or time switch 12. As shown in FIG. 3 the silver plating 8 on a section 1' is in physical engagement with the ribbon links 7 of copper when an electric current is caused to ow through brushes 6, the axially outer ends of fuse links 7 and the portion of silver-plated section 1 sandwiched bctween the axially outer ends of fuse links 7A The aforementioned current causes local fusion of the silver plating 8 on sections 1 where sandwiched between links 7 and the fused silver plating causes parts 1 and 7 to be brazed to each other. On all surface elements of sections 1' not overlapped by copper links 7 the original silver plating remains cool and does not undergo any change during the aforementioned brazing process.

FIG. 4 illustrates one brazed joint between one section or blade contact 1' and the right end of a pair of fuse links 7. Thereupon another silver-plated section or blade contact 1 is sandwiched between the left ends (not shown) of fuse links 7 and the left ends of fuse links 7 are brazed to that section or blade contact 1 in the same way as above described in regard to the right ends of fuse links 7.

FIG. 5 is self-explanatory.

Referring now to FIGS. 6-9 numerals 1 have been applied to indicate a pair of spaced silver-plated blade contacts of copper. Blade contacts 1 are conductively interconnected by a pair of fusible elements '7 in form of copper ribbons each having a plurality of lines of transverse perforations 7a. Each fusible element 7 supports an overlay 7b of tin formed by a strip of tin arranged parallel to the center line of perforations 7a. The axially outer ends of fusible elements 7 overlap, and are brazed to, the axially inner ends of blade contacts 1 in the fashion more fully explained in connection with FIGS. 1 to 5. Each blade contact 1 is provided with a perforation 1a for receiving a pin in the process of further assembly of the fuse. Perforations 1a are in no way obstructe-d by silver spilled over the butt brazing joint between 1 and 7.

As shown in FIGS. 8 and 9 the sub-assembly according to FIGS. 6 and 7 is placed into a tubular casing 14 of insulating material. Both ends of casing 14 are ciosed by caps 15 having rectangular openings 15a through which blade contacts 1 project. Reference numerals 16 have been applied to indicate a pair of asbestos washers having rectangular openings in registry with the rectangular openings lSa in caps 15. Pins 1b project through perforations 1a in blade contacts 1 and through perforations in casing 14 arranged in alignment with perforations 1a. Fuse links 7 are submersed in a pulverulent arc-quenching filler 17 as, for instance, quartz sand.

On occurrence of major fault currents links 7 fuse at their three points of narrowest cross-section formed by their three lines of perforations 7a.

On occurrence of relatively small but protracted overloads tin strips 7b'melt and sever links 7 by causing a metallurgical reaction with the base copper 7.

While in accordance with the patent statutes, I have disclosed the specific details of one embodiment of the invention, it is to be understood that these details are merely illustrative and that many variations thereof may be made without departing from the spirit and scope of the invention. It is my desire, therefore, that the language of the accompanying claims shall be interpreted as broadly as possible and that it be limited only as required by the prior state of the art.

I claim as my invention:

1. An electric fuse comprising a tubular casing of insulating material; a pair of terminal caps closing the ends of said casing; a pair of blade contacts formed by lengths of solid copper bar being entirely silver plated on both surfaces thereof and projecting from the outside of said casing through said pair of terminal caps into the inside of said casing; a ribbon-type fuse link of copper arranged in said casing and having axially outer ends overlapping the axially inner ends of said pair of blade contacts, and conductive means for securing the axially outer ends of said fuse link to the axially in ner ends of said pair of blade contacts, said securing means including brazing joints formed by the silver plating on one of said surfaces c0- extensive with the area of overlap between said fuse link and said pair of blade contacts.

2. An electric fuse comprising a tubular casing of in.- sulating material; a ribbon-type fuse link of copper arranged inside said casing; a pair of terminal caps closing the ends of said casing; a pair of blade contacts formed by lengths of solid copper bar projecting from ythe outside of said casing through said pair of caps into the inside of said casing, the mass of said pair of blade contacts being so large as to inhibit formation of spotwelds between the axially outer ends of said link and the axially inner ends of said pair of blade contacts; a silver pla-ting on the entire area of both surfaces of each of said pair of blade contacts; and conductive means for securing the axially outer ends of said link to the axially inner ends of said pair of blade contacts, said securing means including brazing joints formed by the silver plating on one of said surfaces of said pair of blade contacts coex-tensive with the area of overlap between said fuse link and said pair of blade contacts.

References Cited in the le of this patent UNITED STATES PATENTS 2,021,477 Bohn Nov. 19, 1935 2,250,617 Argentin July 29, 1941 2,641,731 Lines June 9, 1953 2,828,390 McAlister Mar. 25, 1958 2,882,587 Unger et al Apr. 21, 1959 2,988,620 Kozacka June 13, 1961 3,020,372 Kozacka Feb. 6, 1962 

1. AN ELECTRIC FUSE COMPSISING A TUBLAR CASING OF INSULATING MATERIAL, A PAIR OF TERMINAL CAPS CLOSING THE ENDS OF SAID CASING, A PAIR OF BLADE CONTACTS FORMED BY LENGTHS OF SOLID COPPER BAR BEING ENTIRELY SILVER PLATED ON BOTHE SURFACES THEREOF AND PROJECTING FROM THE OUTSIDE OF SAID CASING THROUGH SAID PAIR OF TERMINAL CAPS INTO THE INSIDE OF SAID CASING, A RIBBON-TYPE FUSE LINK OF COPPER ARRANGED IN SAID CASING AND HAVING AXIALLY OUTER ENDS OVERLAPPING THE AXIALLY INNER ENDS OF SAID PAIR OF BLADE CONTACTS, AND CONDUCTIVE MEANS FOR SECURING THE AXIALLY OUTER ENDS OF SAID FUSE LINK TO THE AXIALLY INNER ENDS OF SAID PAIR OF BLADE CONTACTS, AND SECURING MEANS INCLUDING BRAZING JOINTS FORMED BY THE SILVER PLATING ON ONE OF SAID SURFACES COEXTENSIVE WITH THE AREA OF OVERLAP BETWEEN SAID FUSE LINK AND SAID PAIR OF BLADE CONTACTS. 